Method and apparatus for transmitting and receiving in a communication/broadcasting system

ABSTRACT

A method and apparatus for transmitting in a communication/broadcasting system is provided. The method includes determining to use an additional parity technique, generating an Nth parity check matrix, where N is an integer, performing Low Density Parity Check (LDPC) encoding using the Nth parity-check matrix, modulating a codeword corresponding to the Nth parity-check matrix, and transmitting the modulated codeword.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) to KoreanPatent Application Serial No. 10-2011-0018740, which was filed in theKorean Intellectual Property Office on Mar. 3, 2011, the entiredisclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a communication/broadcastingsystem that utilizes a linear code based on a parity-check matrix, andmore particularly, to a method and apparatus for efficiently generatingadditional parity for performance optimization in acommunication/broadcasting system.

2. Description of the Related Art

A communication/broadcasting system performs channel coding in order tocorrect an error occurring in a channel. Although there are a number ofdifferent channel coding methods, these methods can be basically dividedinto methods using a block code, a convolutional code, and aconcatenation code, which concatenates a block code and a convolutionalcode.

The block code was developed based on an error correction theory andincludes a simple linear cyclic code, a Bose, Chaudhuri, Hocquenghem(BCH) code, a Reed-Solomon (RS) code, etc.

For the convolutional code, there is a traditional convolutional codeand a turbo code that is a modification of the traditional convolutionalcode. However, there is also a turbo code that is a modification of thetraditional block code. Therefore, to distinguish between these twocodes, the turbo code based on the convolutional code is called aConvolutional Turbo Code (CTC), and the turbo code based on the blockcode is called a Block Turbo Code (BTC).

Further, there is a Low Density Parity Check (LDPC) code.

Among these codes, the turbo code and the LDPC code, which are alsocalled repetition codes, are Error Correction Codes (ECC) providingpossible error correction closely approaching Shannon's channel capacitylimit.

Presently, the LDPC code approaching Shannon's channel capacity limithas been presented in a broadcasting/communication system.

However, next-generation communication/broadcasting systems will requirethe use of a transmission method capable of maximizing a capacity of anentire system and also meeting demands of various users. Consequently,the use of codes having various code rates and codeword lengths will berequired.

Accordingly, a need exists for a method and apparatus for efficientlysupporting multiple code rates or multiple codewords in acommunication/broadcasting system.

SUMMARY OF THE INVENTION

An aspect of the present invention is to substantially solve at leastthe above-described problems and/or disadvantages and to provide atleast the advantages below.

Accordingly, an aspect of the present invention is to provide a methodand apparatus for transmitting and receiving in acommunication/broadcasting system.

Another aspect of the present invention is to provide an efficientchannel encoding/decoding method and apparatus that support various coderates and various codeword lengths in a communication/broadcastingsystem.

In accordance with an aspect of the present invention, a transmissionmethod of a transmitter in a communication and broadcasting system isprovided. The method includes determining to use an additional paritytechnique, generating an Nth parity check matrix, where N is an integer,performing Low Density Parity Check (LDPC) encoding using the Nthparity-check matrix, modulating a codeword corresponding to the Nthparity-check matrix, and transmitting the modulated codeword.

In accordance with another aspect of the present invention, a receptionmethod of a receiver in a communication and broadcasting system isprovided. The method includes receiving a codeword, performing LowDensity Parity Check (LDPC) decoding for the codeword using an Nthparity-check matrix, where N is an integer, detecting an error in theLDPC decoding, and performing LDPC decoding for the codeword using an(N+1)th parity-check matrix.

In accordance with another aspect of the present invention, an apparatusof a transmitter in a communication and broadcasting system is provided.The apparatus includes a controller for determining to use an additionalparity technique; a parity-check matrix provider for providing an Nthparity check matrix, where N is an integer; a Low Density Parity Check(LDPC) encoder for performing LDPC encoding using the Nth parity-checkmatrix; and a transmitter for modulating a codeword corresponding to theNth parity-check matrix, and transmitting the modulated codeword.

In accordance with another aspect of the present invention, an apparatusof a receiver in a communication and broadcasting system is provided.The apparatus includes a receiving unit for receiving a codeword; aparity-check matrix provider for providing a 2nd parity-check matrixthat is an extension of a 1st parity-check matrix using additionalparity bits, when there is an LDPC decoding error for the codeword; anda Low Density Parity Check (LDPC) decoder for performing LDPC decodingfor the codeword using the 1st parity-check matrix or performing LDPCdecoding for the codeword using the 2nd parity-check matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 illustrates a parity-check matrix according to an embodiment ofthe present invention;

FIG. 2 illustrates a parity-check matrix of N₁=30, K₁=15, M₁=5, q₁=1according to an embodiment of the present invention;

FIG. 3 illustrates a parity-check matrix having a 1st weight-1 sequenceof N₁=32, K₁=12, M₁=4, q₁=5 according to an embodiment of the presentinvention;

FIG. 4 illustrates an extended parity-check matrix according to anembodiment of the present invention;

FIG. 5 is a flowchart illustrating a channel encoding method in acommunication/broadcasting system using an LDPC code according to anembodiment of the present invention;

FIG. 6 is a flowchart illustrating a channel decoding method in acommunication/broadcasting system using an LDPC code according to anembodiment of the present invention;

FIG. 7 illustrates a transmitter according to an embodiment of thepresent invention; and

FIG. 8 illustrates a receiver according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will be described hereinbelow with reference to the accompanying drawings. In the followingdescription, well-known functions or constructions are not described indetail to avoid obscuring the invention in unnecessary detail. Further,terms described below, which are defined considering functions in thepresent invention, can be different depending on user and operatorintention or practice. Therefore, the terms should be defined on thebasis of the disclosure throughout this specification.

Generally, if the flexibility of a code is high, the code can facilitatean Adaptive Modulation and Coding (AMC) technique or a Hybrid AutomaticRetransmission reQuest (HARQ) technique, and support various code ratesand codeword lengths using one COder and DECoder (CODEC), reducinghardware complexity.

In a parity-check matrix ‘H’ or a generation matrix ‘G’ of aparity-check code, when an information word of a length ‘K’, i.e.,composed of ‘K’ bits, is ‘m=(m₀,m₁, . . . ,m_(K−1))’, the informationword satisfies the relationship in m·G=c, H·c ^(T)=0. Here, ‘c’ denotesa codeword acquired from the message ‘m’.

Also, when a codeword of a given linear code is a systematic code, thecodeword ‘c’ is expressed as ‘c=(m, p)’. Here, ‘p’ denotes parity.

Generally, assuming that a message length (i.e., an information wordlength) is ‘K’ and a codeword length is ‘N’, a parity length is ‘(N−K)’and, for full rank, the size of the parity-check matrix ‘H’ is‘(N−K)×N’.

As an example of a systematic code, parity-check matrix ‘H’ as shownEquation (1) below is provided.

$\begin{matrix}{H = \begin{bmatrix}1 & 1 & 1 & 0 & 1 & 0 & 0 \\1 & 1 & 0 & 1 & 0 & 1 & 0 \\1 & 0 & 1 & 1 & 0 & 0 & 1\end{bmatrix}} & (1)\end{matrix}$

Here, a codeword (c) corresponding to the parity-check matrix ‘H’ isconstructed as ‘c=(m, p)’ from an information word ‘m=(m₀,m₁,m₂,m₃)’composed of four information bits and parity ‘p=(p₀, p₁, p₂)’ composedof three parity bits. The codeword (c) is defined in Equation (2) below.

$\begin{matrix}{{H \cdot {\underset{\_}{c}}^{T}} = {{\begin{bmatrix}1 & 1 & 1 & 0 & 1 & 0 & 0 \\1 & 1 & 0 & 1 & 0 & 1 & 0 \\1 & 0 & 1 & 1 & 0 & 0 & 1\end{bmatrix}\begin{bmatrix}m_{0} \\m_{1} \\m_{2} \\m_{3} \\p_{0} \\p_{1} \\p_{2}\end{bmatrix}} = \underset{\_}{0}}} & (2)\end{matrix}$

By arranging Equation (2) as shown in Equation (3) below, each row ofthe parity-check matrix ‘H’ represents one algebraic relationalequation. Each relational equation is called a parity-check equation.

$\begin{matrix}{\begin{bmatrix}{m_{0} + m_{1} + m_{2} + p_{0}} \\{m_{0} + m_{1} + m_{3} + p_{1}} \\{m_{0} + m_{2} + m_{3} + p_{2}}\end{bmatrix} = \begin{bmatrix}0 \\0 \\0\end{bmatrix}} & (3)\end{matrix}$

An element not being ‘0’ in the parity-check matrix is called a weight.In a parity-check code, as the number of weights increases, encoding anddecoding complexity increases. That is, in the entire parity-checkmatrix, as a weight rate decreases, the complexity decreases. Generally,a parity-check code having a very low weight rate is an LDPC code and,in most cases, the LDPC code has a characteristic in which, as acodeword length increases, a weight density decreases.

The parity-check code can be defined differently according to therequirements of a communication and broadcasting system.

FIG. 1 illustrates an example of a parity-check matrix according to anembodiment of the present invention.

Referring to FIG. 1, ‘N₁’ and ‘K₁’ denote a codeword length of aparity-check code and an information word length, respectively, and‘(N₁−K₁)’ denotes a parity length. In the parity-check matrix, a partialmatrix associated with parity, i.e., a structure of K₁ th column to(N₁−1) th column is of a dual-diagonal form.

Accordingly, the number of weights of columns corresponding to thepartial matrix associated with the parity is ‘2’, except for the lastcolumn, which is ‘1’.

A partial matrix associated with an information word, i.e., a 0th columnto a (K₁−1) th column, includes columns that are grouped in units of‘M₁’ columns. Here, ‘M₁’ is a parameter of the parity-check matrix ofFIG. 1, and ‘M₁’ can change a value according to a givencommunication/broadcasting system.

In the partial matrix associated with the information word, if aposition of a row in which a weight exists in a 0th column within eachcolumn group is determined, a position of a row in which a weight existsat in ith column within each column group is cyclically shifted as muchas ‘i·q₁ mod(N₁−K₁)’ from the position of the row in which the weightexists in the 0th column within each column group. Here, the ‘q₁’ is aninteger, and is set to meet ‘q₁=(N₁−K₁)/M₁’.

For example, a parity-check matrix as illustrated in FIG. 1, havingN₁=30, K₁=15, M₁=5, q₁=1 and expressing position information of a rowhaving a weight-1 for each of 0th columns of three column groups as inTable 1 below, is illustrated in FIG. 2.

TABLE 1 0 1 2 0 11 13 0 10 14

Here, the sequence is called a weight-1 position sequence forconvenience. A jth sequence (j=0,1, . . . , (K₁/M₁−1)) in the weight-1position sequence is a sequential expression of position information ofa row in which a weight-1 is positioned at a 0th column within a jthcolumn group in the weight-1 position sequence.

FIG. 2 illustrates a parity-check matrix of N₁=30, K₁=15, M₁=5, q₁=1according to an embodiment of the present invention.

Referring to FIG. 2, in the first column group composed of a 0th columnto a 4th column, weight-1s are positioned in the 0th column, whichcorresponds to the first column within the first column group, in rows0, 1, and 2. Further, weight-1s are positioned in the 1st column, whichcorresponds to the second column within the first column group, in rows3, 4, and 5, where 3 (=(0+q₁)mod(N₁−K₁)), 4 (=(1+q₁)mod(N₁−K₁)), and 5(=(2+q₁)mod(N₁−K₁)). Additionally, weight-1s are positioned in the 3rdcolumn, which corresponds to the fourth column within the first columngroup, in rows 9, 10, and 11, where 9 (=(0+3×q₁)mod(N₁−K₁)), 10(=(1+3×q₁)mod(N₁−K₁), and 11 (=(2+3×q₁)mod(N₁−K₁)).

In the second column group, i.e., the 5th column to the 9th column,weight-1s are positioned at the 5th column, which corresponds to thefirst column within the second column group, in rows 0, 11, and 13.Weight-1s are positioned in the 6th column, which corresponds to thesecond column within the second column group, in rows 1, 3, and 14,where 1 (=(13+q₁)mod(N₁−K₁)), 3 (=(0+q₁)mod(N₁−K₁)), and 14(=(11+q₁)mod(N₁−K₁)). Weight-1s are positioned in the 9th column, whichcorresponds to the fifth column within the second column group, in rows8, 10, and 12, where 8 (=(11+4×q₁)mod(N₁−K₁)), 10(=(13+4×q₁)mod(N₁−K₁)), and 12 (=(0+4×q₁)mod(N₁−K₁)).

Likewise, this feature can be easily identified in the other columngroups.

The parity-check matrix of FIG. 1 can be uniquely defined by N₁, K₁ andM₁ values and weight-1 position sequences. Therefore, for convenience,the parity-check matrix illustrated in FIG. 1 is simply expressed by N₁,K₁, and M₁ weight-1 position sequences corresponding to the parity-checkmatrix.

Assuming that a codeword of the parity-check code associated with theparity-check matrix ‘H’ of Equation (1) is expressed as‘c=(m₀,m₁,m₂,m₃,p₀,p₁,p₂)’ and the ‘c’ is transmitted to a receiving endin a communication/broadcasting system using the parity-check code, thereceiving end may fail to decode an information word ‘m’ from a receivedsignal. In this case, a transmit end transmits additional parity, andthe receive end receives the additional parity, performs combinationwith the code, and again performs decoding to restore the informationword ‘m’.

In accordance with an embodiment of the present invention, a method isprovided for identifying hidden intermediate variables from a givenparity-check matrix and a previously transmitted codeword, and thenutilizing the intermediate values as additional parity in acommunication/broadcasting system. For this, three parity-checkequations, i.e., Equations (i), (ii), and (iii), as expressed inEquation (4) below, are provided.

m ₁ +m ₁ +m ₂ +p ₀=0(i)

m ₀ +m ₁ +m ₃ +p ₁=0(ii)

m ₀ +m ₂ +m ₃ +p ₂=0(iii)  (4)

In Equation (4), Equation ( ) is equivalent to ‘m₀+p₀=m₁+m₂’, Equation(ii) is equivalent to ‘m₀+m₃=m₁+p₁’. Therefore, Equations (i) and (ii)can be expressed as shown in Equation (5) below, introducingintermediate variables (y₀, y₁).

$\begin{matrix} \begin{matrix}{y_{0} = {{m_{0} + p_{0}} = {{m_{1} + m_{2}} = 0}}} \\{y_{1} = {{m_{0} + m_{3}} = {{m_{1} + p_{1}} = 0}}}\end{matrix}\Leftrightarrow\{ \begin{matrix}{y_{0} = {m_{0} + p_{0}}} \\{y_{0} = {m_{1} + m_{2}}} \\{y_{1} = {m_{0} + m_{3}}} \\{y_{1} = {m_{1} + p_{1}}}\end{matrix}   & (5)\end{matrix}$

Equation (6) below provides Equations (4) and (5) expressed asparity-check equations regarding each of the intermediate variables (y₀,y₁) as a parity bit.

$\begin{matrix}{\begin{bmatrix}{m_{0} + p_{0} + y_{0}} \\{m_{1} + m_{2} + y_{0}} \\{m_{1} + p_{1} + y_{1}} \\{m_{0} + m_{3} + y_{1}} \\{m_{0} + m_{2} + m_{3} + p_{2}}\end{bmatrix} = \begin{bmatrix}0 \\0 \\0 \\0 \\0\end{bmatrix}} & (6)\end{matrix}$

In Equation (6) above, there is no change of values of‘m₀,m₁,m₂,m₃,p₀,p₁,p₂’ despite the introduction of the intermediatevariables (y₀, y₁). Also, Equation (6) can be expressed in a form of amultiplication of a matrix as shown in Equation (7) below.

$\begin{matrix}{\underset{\_}{0} = {{\begin{bmatrix}1 & 0 & 0 & 0 & 1 & 0 & 0 & 1 & 0 \\0 & 1 & 1 & 0 & 0 & 0 & 0 & 1 & 0 \\0 & 1 & 0 & 0 & 0 & 1 & 0 & 0 & 1 \\1 & 0 & 0 & 1 & 0 & 0 & 0 & 0 & 1 \\1 & 0 & 1 & 1 & 0 & 0 & 1 & 0 & 0\end{bmatrix}\begin{bmatrix}m_{0} \\m_{1} \\m_{2} \\m_{3} \\p_{0} \\p_{1} \\p_{2} \\y_{0} \\y_{1}\end{bmatrix}} = {H_{E} \cdot {\underset{\_}{c}}_{E}^{T}}}} & (7)\end{matrix}$

In Equation (7), ‘c _(E)’ represents a codeword composed of ‘c’ and ‘y₀,y₁’. Here, a parity-check matrix for the codeword ‘c _(E)’ is ‘H_(E)’.That is, it is the same as generating an extended codeword ‘c _(E)=(c, y₀, y ₁)’ in which parity (y₀, y₁) are additionally added to the firstlygiven codeword ‘c’.

Here, in the relationship between the ‘H’ of Equation (1) and the‘H_(E)’ of Equation (7), the first row of the ‘H’ is determined bycombining the first and second rows of the ‘H_(E)’, and the second rowof the ‘H’ is determined by combining the third and fourth rows of the‘H_(E)’.

If rows of the parity-check matrix ‘H_(E)’ determined through theintroduction of the intermediate variables as above are suitably addedto each other, the firstly given parity-check matrix ‘H’ can bedetermined as desired.

When a communication/broadcasting system uses a parity-check code forencoding/decoding, and suitable intermediate variables are introducedinto a parity-check matrix of the parity-check code as in Equations (4)and (5) above, the communication/broadcasting system can determine anextended parity-check matrix like ‘H_(E)’ in Equation (7) and theintroduced intermediate variables can be regarded as newly generatedparity bits. Accordingly, when the communication/broadcasting systemrequires transmission of additional parity, thecommunication/broadcasting system can transmit values corresponding tothe intermediate variables and perform efficient encoding/decoding.

Commonly, when a communication/broadcasting system uses additionalparity, the communication/broadcasting system cannot determine anadditional coding gain until generating new additional parity differentfrom previously generated parity, rather than simply repeatedlytransmitting parity. However, in accordance with an embodiment of thepresent invention, the communication/broadcasting system can achieveadditional coding gain by generating the additional parity usingEquations (4) and (5), as described above.

Generally, when a communication/broadcasting system separates each of‘A’ parity-check equations into two parity-check equations anddetermines ‘2A’ parity-check equations in a parity-check matrix, thecommunication/broadcasting system can draw ‘A’ intermediate variables.

For example, as shown in Equations (4), (5), and (7), when thecommunication/broadcasting system separates each of two parity-checkequations matching with two rows into two parity-check equations in agiven parity-check matrix, the total two intermediate variables aredrawn.

Additionally, each time one parity-check equation is separated into ‘B’parity-check equations, the communication/broadcasting system can draw‘(B−1)’ intermediate variables.

Generally, when each of ‘A’ parity-check equations is separated into ‘B’parity-check equations and ‘A·B’ parity-check equations are determined,the communication/broadcasting system can draw a total of ‘A·(B−1)’intermediate variables.

Although an embodiment of the present invention wherein a parity-checkequation is separated into two parity-check equations, i.e., where‘B=2’, the value of ‘B’ is not limited thereto. That is, theparity-check equation may be separated into a different number ofparity-check equations.

In accordance with an embodiment of the present invention, a method isprovided, which uses additional parity through a hidden intermediatevariable determined using Equations (4) and (5) according to a specificrule in a parity-check matrix as illustrated in FIG. 1 for an LDPC codehaving the parity-check matrix of FIG. 1. Further, an efficient encodingmethod for the LDPC code is provided.

First, an example of an encoding method for an LDPC code having theparity-check matrix of FIG. 1 is provided. Here, the parity-check matrixis ‘H₁’, a partial matrix associated with an information word part is‘H_(1,I)’, and a partial matrix associated with parity is ‘H_(1,P)’.That is, H₁=[H_(1,I) H_(1,P)]. Also, a codeword ‘c ₁’ is given as ‘c₁=(m, p ₁)’ using a message ‘m’ and parity ‘p ₁’.

The codeword ‘c ₁’ should meet ‘H₁·c ₁ ^(T)=0’ and therefore, can bearranged as shown in Equation (8) below.

$\begin{matrix}{\underset{\_}{0} = { {\begin{bmatrix}H_{1,I} & H_{1,P}\end{bmatrix} \cdot \begin{bmatrix}\underset{\_}{m} \\{\underset{\_}{p}}_{1}\end{bmatrix}}\Rightarrow{H_{1,I}{\underset{\_}{m}}^{T}}  = {H_{1,P}{\underset{\_}{p}}_{1}^{T}}}} & (8)\end{matrix}$

Accordingly, the encoding process of the LDPC code is the same asgenerating the parity ‘p ₁’ of Equation (8).

As an example of this encoding process, a method for generating theparity ‘p ₁’ associated with the parity-check matrix ‘H₁’ of FIG. 1 isas follows.

Example of Encoding Method

-   -   Step 1) Initializing to get p ₁=(p_(1,0),p_(1,1), . . .        ,p_(1,(N) ₁ _(−K) ₁ ⁻¹⁾=0 (p_(1,0),p_(1,1), . . . ,p_(1,(N) ₁        _(−K) ₁ ⁻¹⁾=0)    -   Step 2) Storing to get p ₁=H_(1,l),m ^(T)    -   Step 3) Sequentially taking p_(1,i)←p_(1,j)⊕p_(1,j−1) for i=1,2,        . . . , (N₁−K₁−1). Here, the ‘⊕’ is an eXclusive OR(XOR)        operation.

A method for determining an extended parity-check matrix by introducingsuitable intermediate variables as in Equations (4) and (5) for theparity-check matrix ‘H₁’ is defined as follows. Here, a first givenparity-check matrix is called a 1st parity-check matrix, and itscorresponding weight-1 position sequence is called a 1st weight-1position sequence.

Method for Determining Extended Parity-Check Matrix

A position (a₀,a₁,a₂, . . . ,a_(F) _(IR) ⁻¹) of a row corresponding to aparity-check equation to be separated in a parity-check matrixcorresponding to a 1st weight-1 sequence is determined, where each a₁value satisfies the relationship of 0≦a₀≦a₁≦ . . . ≦a_(F) _(IR) ⁻¹<q₁.

For i=0,1, . . . , (F_(IR)−1), j=0,1, . . . , (M₁−1), all parity checkequations corresponding to a a_(i+j·q) ₁ th row are separated byapplying hidden intermediate variables determined using Equations (4)and (5).

The parity-check matrix determined through parity check Equation (ii)above is called a 2nd parity check matrix, and its correspondingweight-1 position sequence is called a 2nd weight-1 position sequence.

FIG. 3 illustrates a parity-check matrix having a 1st weight-1 sequenceof N₁=32, K₁=12, M₁=4, q₁=5 according to an embodiment of the presentinvention.

Referring to FIG. 3, a parity-check matrix ‘H₁’ being N₁=32, K₁=12,M₁=4, q₁=5 and having a 1st weight-1 sequence shown in Table 2 isprovided.

TABLE 2 0 8 12 18 1 4 14 0 11 17

Assuming that F_(IR)=2 and a₀=3, a₁=4 are previously determined, aparity-check matrix as illustrated in FIG. 4 can be determined.

FIG. 4 illustrates an extended parity-check matrix according to anembodiment of the present invention.

Referring to FIG. 4, the extended parity-check matrix of FIG. 4 can bedetermined by separating parity check equations corresponding to a(3+5i)th row and a (4+5i)th row for i=0, 1, 2, 3 from the parity-checkmatrix illustrated in FIG. 3.

A 2nd weight-1 position sequence is given in Table 3 below.

TABLE 3 0 10 16 25 1 5 20 0 15 23

Assuming parity ‘p=(p₀, p₁, . . . , p₁₉)’ corresponding to the 1stparity-check matrix ‘H₁’ of FIG. 3 and parity p _(E)=(p_(E,0), p_(E,1),. . . , p_(E,27)) corresponding to the 2nd parity-check matrix ‘H_(E)’of FIG. 4, the following relationship is established.

Regarding i=0, 1, 2, 3, P_(E,(0+7i))=P_(0+5i), p_(E,(1+7i))=p_(1+5i),P_(E,(2+7i))=p_(2+5i), P_(E,(4+7i))=p_(3+5i), p_(E,(6+7i))=p_(4+5i) areestablished, and p_(E,(3+7i)) and p_(E,(5+7i)) are newly generatedparity. Here, the number of newly generated parity bits is equal to 8bits from ‘2×4(=F_(IR)×M₁=N_(IR))’.

Here, it is assumed that there is a need to transmit additional paritybits of the 8 bits, after applying the Example of Encoding Method basedon the 1st parity-check matrix illustrated in FIG. 3, generating acodeword, and transmitting the codeword to a receiver.

To generate the 8 additional parity bits, a codeword is generated byapplying the Example of Encoding Method based on the 2nd parity-checkmatrix illustrated in FIG. 4.

Thereafter, if only the newly generated parity bits not corresponding tothe codeword generated based on the 1st parity-check matrix areselectively transmitted, that is, if only the newly generated parity aretransmitted, the receiver can perform decoding using the codewordgenerated based on the 1st parity-check matrix and the 8 additionalparity bits.

However, because simply twice performing the Example of Encoding Methodgenerates many unnecessary redundant parity bits, resources are wastedand an encoding delay occurs. This phenomenon increases as a code rateof an LDPC code is lowered and as the number of parity bits toadditionally generate increases.

Accordingly, the following modified encoding method is provided.

Here, a 1st parity-check matrix is given as H₁=[H_(1,l) H_(1,P)], andkey parameters of a code are given as a codeword length ‘N₁’, aninformation word length ‘K₁’, a column group unit ‘M₁’, ‘q₁=(N₁−K₁)/M₁’.A 2nd parity-check matrix determinable from the 1st parity-check matrixby applying the Method for Determining Extended Parity-Check Matrix isgiven as H_(E)=[H_(E,l) H_(E,P)], and key parameters of each code aregiven as ‘N_(E)=(N₁+N_(IR))’, an information word length ‘K₁’, a columngroup unit ‘M₁’, and ‘q_(E)=(N_(E)−K₁)/M₁’.

Here, the ‘N_(IR)’ indicates the number of parity bits to be newly addedand, to guarantee that the ‘q_(E)’ is an integer, ‘N_(IR)/M₁=F_(IR)’(however, F_(IR)≦q₁) is set to be an integer. Also, each codeword isexpressed as c ₁=(m, p ₁)=(m, p_(1,0), p_(1,1), . . . , p_(1,(N) ₁ _(−K)₁ ⁻¹⁾), and c _(E)=(m, p_(E))=(m, p_(E,0), p_(E,1), . . . , p_(E,(N) ₁_(−K) ₁ ⁻¹⁾).

Modified Encoding Method

Step 1) Initializing to get p_(E,0) = p_(E,1) = ... = p_(E,(N) ₁−K₁−1) =0 Step 2) Storing to get p _(E) = H_(E,I),m ^(T) Step 3)     Temp = 0;    For 0 ≦ i < M_(l)       For 0 ≦ j < q_(E)         p_(E,(i·q) _(E)_(+j+1)) ← p_(E,(i·q) _(E) _(+j+1)) ⊕ p_(E,(i·q) _(E) _(+j))         For0 ≦ k < F_(IR)           If ((i · q_(E) + j) ≠ (i · q_(E) + a_(k) + 1))           p_(1,i·q) _(E) _(+j−Temp) = p_(E,i·q) _(E) _(+j)          Else            Temp ← (Temp + 1)         End       End    End

The Modified Encoding Method can generate ‘c ₁’ and ‘c _(E)’simultaneously.

Accordingly, when a transmitting end generates and transmits additionalparity bits, after transmitting ‘c ₁’, it is sufficient for thetransmitting to additionally transmit only ‘p_(E,a) ₁ _(+j·q) _(E) ’ fori=0,1, . . . , (F_(IR)−1), j=0,1, . . . ,(M₁−1) in ‘c _(E)’, withouthaving to again generate the whole ‘c _(E)’.

Generally, when a system does not apply an additional parity technique,the Example of Encoding Method is efficient and, when the system appliesthe additional parity technique, the Modified Encoding Method isefficient. Therefore, it is desirable to determine the encoding methodaccording to whether or not the additional parity technique is applied.

FIG. 5 is a flowchart illustrating a channel encoding method in acommunication/broadcasting system using an LDPC code according to anembodiment of the present invention.

Referring to FIG. 5, in step 500, a transmitter determines whether toapply an additional parity technique. Here, the determination criterioncan be different according to a realization situation or channel state,or can be previously set.

When applying the additional parity technique, in step 510, thetransmitter generates a 2nd parity-check matrix from a 1st parity-checkmatrix.

Step 510 may be repeatedly performed several times. For example, thetransmitter can generate a 3rd parity-check matrix using a 2ndparity-check matrix and, likewise, can generate an Nth parity-checkmatrix using an (N−1)th parity-check matrix. Further, if the transmitterhas already stored the 2nd, 3rd, . . . , Nth parity-check matrixes usinga memory, step 510 may be omitted.

In step 520, the transmitter performs encoding using the generated 2ndparity-check matrix. When the transmitter has generated the Nthparity-check matrix as above, it is also possible to perform encodingusing the Nth parity-check matrix.

In step 530, the transmitter modulates and transmits a codewordcorresponding to the 1st parity-check matrix. If the transmittergenerates the Nth parity-check matrix in step 510, the transmitter mayseparately transmit each of additional parity bits generatedsequentially up to the Nth parity-check matrix.

As described above, the transmitter may separately transmit theadditional parity bits in time, but may also separately transmit inspace or in frequency. For example, in step 540, the transmitter mayseparately transmit the additional parity bits through a different frameor a different region of a specific transmission duration transmitted atan equal time, or may transmit through a different frequency band.

If it is determined in step 500 that the transmitter will not apply theadditional parity technique, in step 550, the transmitter performsencoding using the 1st parity-check matrix. In step 560, the transmitterthen modulates and transmits a codeword corresponding to the 1stparity-check matrix.

FIG. 6 is a flowchart illustrating a channel decoding method in acommunication/broadcasting system using an LDPC code according to anembodiment of the present invention.

Referring to FIG. 6, in step 600, a receiver receives an encodinginformation bit and, in step 602, performs LDPC decoding using a 1stparity-check matrix.

If the receiver determines that there is no LDPC decoding error in step604, the method returns to step 600, such that the receiver cancontinuously receive an encoding information bit and then re-performLDPC decoding using the 1st parity-check matrix in step 602.

However, the receiver determines that there is an LDPC decoding error instep 604, in step 606, and the receiver sends a request for transmissionof additional parity to a transmitter, receives additional parity bitsfrom the transmitter, and generates a 2nd parity-check matrix using thereceived additional parity bits.

Alternatively, the receiver may already have stored or generated the 1stparity-check matrix and the 2nd parity-check matrix. In this case, thereceiver may then determine additional parity bits using the 1st and 2ndparity-check matrixes stored or generated in the receiver, withoutrequesting and receiving the additional parity bits. Further,irrespective of the request from the receiver, the transmitter maytransmit the additional parity bits to the receiver, and the receivermay store the additional parity bits transmitted from the transmitterand use, if there occurs a decoding error, the stored additional paritybits without a separate request.

In step 608, the receiver performs LDPC decoding using the 2ndparity-check matrix, which is an extension of the 1st parity-checkmatrix.

Although not illustrated separately, when a receiver of excellentdecoding performance in which performance is not deteriorated, even whendecoding is performed using an extended Nth parity-check matrix, ratherthan the 1st parity-check matrix, the receiver can omit steps 602, 604,and 606 and just perform the decoding using the Nth parity-check matrix.

The Nth parity-check matrix may be acquired from the transmitter or maybe previously stored in the receiver.

In this case, the transmitter suitably encodes and transmits using theNth parity-check matrix, or the transmitter encodes using a 1stparity-check matrix and, separately or together with encoded data,transmits additional parity bits generated sequentially up to the Nthparity-check matrix.

Also, even when transmitted data or content require high decodingperformance as premium data or content, the receiver can omit steps 602,604, and 606 and just perform decoding using an Nth parity-check matrix.That is, when the transmitter encodes and transmits the data or contentas the premium data or content using the Nth parity-check matrix, orwhen the transmitter performs encoding using a 1st parity-check matrixand transmits, separately or together with encoded data, additionalparity bits generated sequentially up to the Nth parity-check matrix,the receiver can omit steps 602, 604, and 606 and just perform thedecoding using the Nth parity-check matrix or perform the decoding usingthe additional parity bits generated sequentially up to the Nthparity-check matrix.

FIG. 7 illustrates a transmitter according to an embodiment of thepresent invention.

Referring to FIG. 7, the transmitter includes an LDPC encoder 700, atransmitter 702, a parity-check matrix provider 704, and a controller706. The LDPC encoder 700 performs LDPC encoding using a 1stparity-check matrix or 2nd parity-check matrix provided from theparity-check matrix provider 704. For example, LDPC encoder 700 receivesan input information signal ‘m=(m₀, m₁, . . . ,m_(k−1))’, and outputs acodeword ‘c’ meeting ‘H·c ^(T)=0’ for a parity-check matrix ‘H’.

The parity-check matrix provider 704 provides a suitable parity-checkmatrix to the LDPC encoder 700 according to the determination of thecontroller 706 as to whether to apply an additional parity technique.

The parity-check matrix provider 704 can either generate a 2ndparity-check matrix through a 1st parity-check matrix or store the 1stand 2nd parity-check matrixes, and provides the 1st parity-check matrixor 2nd parity-check matrix to the LDPC encoder 700 according to thedetermination of the controller 706.

The parity-check matrix provider 704 can provide additional parity bitsgenerated sequentially up to an Nth parity-check matrix, to the LDPCencoder 700 or the transmitter 702.

When the parity-check matrix provider 704 simultaneously provides the1st or 2nd parity-check matrix and the generated additional parity bitsto the LDPC encoder 700, the LDPC encoder 700 provides the received 1stor 2nd parity-check matrix, a codeword generated through an informationbit, and the additional parity bits, to the transmitter 702.

The additional parity bits may be arranged and encoded in a differentframe or a different region within the same frame. Although notillustrated, the additional parity bits may be provided directly to thetransmitter 702.

The transmitter 702 modulates an encoded bit received from the LDPCencoder 700 and then, frequency-up converts a baseband signal into aRadio Frequency (RF) signal and transmits the RF signal through anantenna.

When the transmitter 702 is provided with additional parity bits fromthe parity-check matrix provider 704, the transmitter 702 can transmitthe additional parity bits through a different frequency band, adifferent time, or a different frame.

FIG. 8 illustrates a receiver according to an embodiment of the presentinvention.

Referring to FIG. 8, the receiver includes a receiver 800, an LDPCdecoder 802, a feedback unit 804, and a parity-check matrix provider806.

The receiver 800 frequency-down converts a Radio Frequency (RF) signalreceived through an antenna into a baseband signal and demodulates thebaseband signal.

When additional parity bits have been transmitted through a differentfrequency band, a different time, or a different frame, the receiver 800can separately separate the additional parity bits and provide theadditional parity bits to the LDPC decoder 802.

The LDPC decoder 802 performs decoding associated with encodingperformed by the LDPC encoder 700 illustrated in FIG. 7, based on a 1stparity-check matrix or 2nd parity-check matrix provided from theparity-check matrix provider 806.

Also, the LDPC decoder 802 can perform decoding using additional paritybits provided from the receiver 800 or the parity-check matrix provider806 and a parity-check matrix provided from the parity-check matrixprovider 806.

When the LDPC decoder 802 performs the decoding associated with theencoding performed by the LDPC encoder 700, the LDPC decoder 802 informsthe decoding result of the feedback unit 804. That is, when an erroroccurs while decoding, the LDPC decoder 802 provides a NegativeACKnowledgement (NACK) signal to the feedback unit 804 and, when normalprocessing is performed at the time of decoding, the LDPC decoder 802provides an ACKnowledgement (ACK) signal to the feedback unit 804.

The feedback unit 804 transmits an ACK/NACK signal to a transmitter.When reverse transmission is impossible, as in many broadcastingstandards, the feedback unit 804 may not be an essential element.

The parity-check matrix provider 806 can either generate a 2ndparity-check matrix through a 1st parity-check matrix or store the 1stand 2nd parity-check matrixes, and provides the 1st or 2nd parity-checkmatrix to the LDPC decoder 802.

The parity-check matrix provider 806 can provide additional parity bitsgenerated sequentially up to an Nth parity-check matrix, to the LDPCdecoder 802.

When the parity-check matrix provider 806 simultaneously provides the1st parity-check matrix or 2nd parity-check matrix and the generatedadditional parity bits to the LDPC decoder 802, the LDPC decoder 802performs decoding using the additional parity bits and the parity-checkmatrix.

When the additional parity bits are arranged and encoded in a differentframe or a different region within the same frame, but are notseparately provided from the parity-check matrix provider 806, theadditional parity bits can be acquired from the receiver 800 or the LDPCdecoder 802.

As described above, the various embodiments of the present invention canefficiently support a multiple code rate or a multiple codeword, bymodifying a parity-check matrix of a parity-check code or LDPC code andusing additional parity-check bits in a communication/broadcastingsystem using the parity-check code or LDPC code. Consequently, anencoding/decoding complexity is reduced, and a decoding convergencespeed increased, thereby improving performance.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims and their equivalents.

1. A transmission method of a transmitter in a communication andbroadcasting system, the method comprising: determining to use anadditional parity technique; generating an Nth parity check matrix,where N is an integer; performing Low Density Parity Check (LDPC)encoding using the Nth parity-check matrix; modulating a codewordcorresponding to the Nth parity-check matrix; and transmitting themodulated codeword.
 2. The method of claim 1, further comprisingseparately transmitting each of additional parity bits generatedsequentially up to the Nth parity-check matrix.
 3. The method of claim1, wherein performing the LDPC encoding comprises: receiving an inputinformation signal ‘m=(m₀,m₁, . . . ,m_(k−1))’; and outputting acodeword ‘c’, where ‘c’ satisfies ‘H·c ^(T)=0’ for a parity-check matrix‘H’.
 4. The method of claim 1, wherein generating the Nth parity checkmatrix comprises: previously storing 1st, 2nd, 3rd, . . . , Nthparity-check matrixes; and retrieving the Nth parity-check matrix fromthe previously stored N parity-check matrixes.
 5. The method of claim 1,wherein generating the Nth parity check matrix comprises: selecting atleast one parity check equation corresponding to a parity check equationin an (N−1)th parity-check matrix; separating each of the selected atleast one parity check equation into at least two parity checkequations; and arranging the separated parity check equations into theNth parity-check matrix.
 6. A reception method of a receiver in acommunication and broadcasting system, the method comprising: receivinga codeword; performing Low Density Parity Check (LDPC) decoding for thecodeword using an Nth parity-check matrix, where N is an integer;detecting an error in the LDPC decoding; and performing LDPC decodingfor the codeword using an (N+1)th parity-check matrix.
 7. The method ofclaim 6, further comprising generating additional parity bits using theNth and (N+1)th parity-check matrixes stored or generated in thereceiver.
 8. The method of claim 6, further comprising generating the(N+1)th parity-check matrix from the Nth parity-check matrix usingadditional parity bits received from a transmitter.
 9. The method ofclaim 6, wherein the Nth parity-check matrix is a matrix acquired fromthe transmitter or is a matrix previously stored in the receiver. 10.The method of claim 6, wherein the (N+1)th parity-check matrix isgenerated using an Nth parity-check matrix by: selecting at least oneparity check equation corresponding to a parity check equation in theNth parity-check matrix; separating the selected at least one paritycheck equation into at least two parity check equations, respectively;and arranging the separated parity check equations into the (N+1)thparity-check matrix.
 11. An apparatus for transmitting in acommunication and broadcasting system, the apparatus comprising: acontroller for determining to use an additional parity technique; aparity-check matrix provider for providing an Nth parity check matrix,where N is an integer; a Low Density Parity Check (LDPC) encoder forperforming LDPC encoding using the Nth parity-check matrix; and atransmitter for modulating a codeword corresponding to the Nthparity-check matrix, and transmitting the modulated codeword.
 12. Theapparatus of claim 11, wherein the parity-check matrix providerseparately transmits each of additional parity bits generatedsequentially up to the Nth parity-check matrix.
 13. The apparatus ofclaim 11, wherein the LDPC encoder receives an input information signal‘m=(m₀,m₁, . . . ,m_(k−1))’ and outputs a codeword ‘c’, where ‘c’satisfies ‘H·c ^(T)=0’ for a parity-check matrix ‘H’.
 14. The apparatusof claim 11, wherein the transmitter previously stores 1st, 2nd, 3rd, .. . , Nth parity-check matrixes, the parity-check matrix providerretrieves the Nth parity-check matrix from the previously stored Nparity-check matrixes.
 15. The apparatus of claim 11, wherein theparity-check matrix provider generates the Nth parity check matrix byselecting at least one parity check equation corresponding to a paritycheck equation in an (N−1)th parity-check matrix, separating each of theselected at least one parity check equation into at least two paritycheck equations, and arranging the separated parity check equations intothe Nth parity-check matrix.
 16. An apparatus for receiving in acommunication and broadcasting system, the apparatus comprising: areceiving unit for receiving a codeword; a parity-check matrix providerfor providing a 2nd parity-check matrix that is an extension of a 1stparity-check matrix using additional parity bits, when there is an LDPCdecoding error for the codeword; and a Low Density Parity Check (LDPC)decoder for performing LDPC decoding for the codeword using the 1stparity-check matrix or performing LDPC decoding for the codeword usingthe 2nd parity-check matrix.
 17. The apparatus of claim 16, wherein theparity-check matrix provider generates the additional parity bits usingthe 1st and 2nd parity-check matrixes stored or generated in thereceiver.
 18. The apparatus of claim 16, wherein, after receiving thecodeword, the LDPC decoder performs LDPC decoding for the codeword usingan Nth parity-check matrix.
 19. The apparatus of claim 18, wherein theNth parity-check matrix is acquired from the transmitter or ispreviously stored in the receiver.
 20. The apparatus of claim 18,wherein the parity-check matrix provider generates the Nth parity-checkmatrix using an (N−1)th parity-check matrix by selecting at least oneparity check equation corresponding to a parity check equation in the(N−1)th parity-check matrix, separates each of the selected at least oneparity check equation into at least two parity check equations, andarranges the separated parity check equations into the Nth parity-checkmatrix.